June has been declared National Oceans Month, via a writ from the White House a few days ago, and this week communities around the planet will mark World Oceans Day.

The flurry of recognition seems appropriate for a region that covers 70 percent of the Earth's surface and provides about half the air we breathe, courtesy of the microscopic, oxygen-producing phytoplankton floating in it.

Yet much about the planet's oceans remains a mystery. As of the year 2000, the National Oceanic and Atmospheric Administration (NOAA) estimated that as much as 95 percent of the world's oceans and 99 percent of the ocean floor are unexplored.

Exploring these regions deep below the ocean's surface is difficult, time-consuming and expensive. Which hasn't stopped people from trying — and making incredible discoveries along the way.

NOAA Okeanos, INDEX-SATAL 2010

A deep-dwelling sea cucumber swimming in the frigid waters of the abyss, roughly 10,500 feet deep.

Known unknowns
Shallower parts of the ocean, and those closer to coastline, have understandably gotten the lion's share of investigation.

What's been fairly well explored is about one Washington Monument down into the ocean — about 556 feet — said Mike Vecchione, a veteran scientist with NOAA and the Smithsonian Institution.

Impressive, perhaps, yet the average depth of the planet's oceans is 13,120 feet, the height of many peaks in the Rockies and the Alps.

"In the deep ocean we're still exploring, and frankly, that's most of the planet that we live on. And we're still in the exploratory phase," Vecchione told OurAmazingPlanet.

Although hard numbers are difficult to pin down, the ocean possesses more than 90 percent of the living space on the planet, perhaps as much as 99 percent, Vecchione said — which means that landlubbers like humans or parakeets or armadillos are rare exceptions in a world of ocean dwellers.

Kevin Raskoff, MBARI, NOAA / OER

Light refracts off a comb-jelly, a species found in the Arctic, producing stripes of rainbow color. Polar waters are home to many species seen nowhere else on Earth.

Deep sea discoveries
Humans are familiar with all sorts of coastal ocean creatures (from crabs to seaweed), coral reef denizens (from clownfish to coral itself), and the bigger, charismatic fauna of the sea (dolphins and whales). But the picture of a whole strange world of life in the deep, dark waters of the world's oceans is slowly emerging.

"People used to think that biodiversity dropped off as you got deeper and deeper in the ocean, but that was just because it's harder and harder to catch things as you get deeper," said Ron O'Dor, a professor at Dalhousie University in Canada, and one of the senior scientists for the Census of Marine Life, a decade-long international study of the planet's oceans that uncovered more than 1,200 new species, excluding microbes, since the project began in 2000.

Seafaring robots are fueling some of that discovery. Remotely Operated Vehicles (ROVs), which are tethered to ships, and more recently, Autonomous Underwater Vehicles (AUVs), which roam freely, collecting visuals and samples during jaunts dictated by computer programs, have made exploration more efficient, O'Dor said.

However, O'Dor told OurAmazingPlanet, even the best robots can't totally replace humans.

Pictures on computer screens are great, "but that's still not the same as having somebody come back from the deep sea and having them describe it to you," O'Dor said.

Humans in the depths
Vechionne can do just that. In 2003, he was one of the first humans to descend into one of the deepest spots on Earth, the Charlie-Gibbs Fracture Zone, a gash in the mid-Atlantic seafloor that is 14,760 feet at its deepest.

During the dive he spied something out of the corner of his eye — a dumbo octopus.

"I was able to tell the pilot to turn around, and we got some really great video," Vechionne said, something that wouldn't have happened without humans aboard.

Although he witnessed the wonders of the deep sea firsthand, Vechionne said it's important to use all the tools available for exploration, because much is lurking out of sight in the darkness. A new species of squid, for example.

Vechhione pointed to the discovery of the bigfin squid about 10 years ago, a pale, leggy creature that can reach up to 21 feet in length and would look right at home in a 1960s B-movie.

"It was exciting when we first discovered them," Vechionne said. "I was jumping up and down in my office."

The squid were caught on film, thanks to ROVs. And if such huge creatures eluded discovery until recently, both Vechhione and O'Dor said, what else is out there?

Yet sending anything to the ocean depths, human or machine, is expensive, and both scientists said funding is a constant issue.

U.S. Naval History & Heritage Command.

The Trieste prepares for mid-Pacific operations in 1959. The vessel took two humans to the deepest spot on Earth — the Mariana Trench in the western Pacific Ocean — in 1960. It was an eye-popping 36,200 feet below the surface — more than a mile deeper than Mount Everest is tall. To this day, the dive has been unmatched.

Private sector dives?
Enter British tycoon Richard Branson, who announced plans earlier this year to send humans, aboard newfangled submersibles, to the five deepest spots on Earth.

The deepest is the Mariana Trench in the western Pacific Ocean, an eye-popping 36,200 feet below the surface — more than a mile deeper than Mount Everest is tall. Humans have visited this trench only once, in 1960, when the Trieste, a deep-diving craft purchased by the U.S. Navy, spent about 20 minutes parked on the ocean floor.

The two humans aboard the Trieste were U.S. Navy Lt. Don Walsh and Swiss scientist Jacques Piccard, co-designer of the remarkable vessel. To this day, their dive has been unmatched.

More humans, 12 in all, have walked on the moon than have traveled to the deepest parts of our own planet.

O'Dor said discovery is important for its own sake, but humans have a vested interest in what is happening to the oceans we depend on for air, food and transport, among other things.

"Not only is there a lot out there left to discover, but there's a lot that's changing, and we need to more or less routinely keep track of those changes," O'Dor said. "To quantify and document them."

The oceans cover more than 70 percent of the earth's surface, yet their depths remain largely unknown. It's a frontier that scientists are racing to explore using tools such as the deep-ocean submersible Alvin, shown here. Click the "Next" arrow above to learn about 10 deep-ocean secrets that have come to light.

Deep-ocean octopuses have Antarctic origins

Census of Marine Life

Many deep ocean octopuses trace their origins back to relatives that swam in the waters around Antarctica. The migration began about 30 million years ago when the continent cooled and large ice sheets grew, forcing octopuses there into ever deeper waters. The climate shift also created a northbound flow of deep, cold water that carried the cephalopods to new habitats. As they adapted to new niches, new species evolved. Many lost their defensive ink sacs because the pitch-black ocean depths required no camouflage screen. The species known as Megaleledon setebos, shown here, is the closest living relative of the deep-sea octopuses' common ancestor.

The orange and red starfish relatives called brittlestars have managed to defy the odds and colonize the flanks of a giant, underwater peak on the Macquarie Ridge, an 870-mile-long underwater mountain range that stretches south from New Zealand to just short of the Antarctic Circle. The peak, known as a seamount, juts up into a swirling circumpolar current that flows by at 2.5 miles per hour, delivering ample food for the brittlestars to grab while sweeping away fish and other would-be predators. Another brittlestar species has settled on the seamount's flat summit, a habitat normally settled by corals and sponges.

Deep Antarctic waters, cradle of marine life

Wiebke Brokeland / GCMB

This pale crustacean from the genus Cylindrarcturus is one of more than 700 species new to science found scurrying, scampering and swimming in the frigid waters between 2,000 and 21,000 feet below the surface of the Weddell Sea off Antarctica. The discoveries were part of a research project to determine how species at different depths are related to each other there, and to other creatures around the world. "The Antarctic deep sea is potentially the cradle of life of the global marine species," team leader Angelika Brandt, an expert from the Zoological Institute and Zoological Museum at the University of Hamburg, said in a statement announcing the discoveries.

Northernmost black smokers discovered

Credit: Center for Geobiology/U. of Bergen

Scientists working deep inside the Arctic Circle have discovered a cluster of five hydrothermal vents, also known as black smokers, which spew out liquid as hot as 570 degrees Fahrenheit. The vents are 120 miles further north than the closest known vents, which tend to occur where the seafloor spreads apart at a quicker pace. This image shows the arm of a remotely operated vehicle reaching out to sample fluids billowing from the top three feet of the tallest vent, which reaches four stories off the seafloor. The chimney is covered with white bacteria that feast on the freshly delivered minerals.

The discovery of primitive bacteria on 1.43 billion-year-old black-smoker fossils – a crosscut is shown here – unearthed from a Chinese mine adds weight to the idea that life may have originated in deep-sea hydrothermal vents, according to geologist Timothy Kusky at Saint Louis University. The ancient microbe dined on metal sulfide that lined the fringes of the chimneys. The oldest-known life forms on Earth are 3.5 billion-year-old clumps of bacteria found in Western Australia. That find suggested that shallow seas, not the deep oceans, were the birthplace of life. Neither discovery, however, serves as the definitive answer about life's origins.

Microbes feast on ocean-bottom crust

NOAA/WHOI

Once thought barren and sparsely populated, the deep-ocean floor is home to rich and diverse communities of bacteria. In fact, scientists have found that the seafloor contains three to four times more bacteria than the waters above, raising the question of how the organisms survive. Lab analyses suggest that chemical reactions with the rocks themselves provide the fuel for life. The discovery is another tantalizing hint that life could have originated in the ocean depths. In a statement about the find, the University of Southern California's Katrina Edwards said: "I hope that people turn their heads and notice: There's life down there."

Where do deep-sea fish go to spawn?

Harbor Branch / E.widder

Life in the dark, cold and vast depths of the sea was long thought to be lonely for the few fish that dared eke out an existence there, mostly from organic detritus that sinks from shallower waters. That picture began to change in 2006, when researchers probing the Mid-Atlantic Ridge discovered that fishes may occasionally gather at features such as seamounts to spawn. The evidence for these gatherings comes from the sheer volume of fish collected at seamounts – much higher than would have been expected if the fish were purely nomadic wanderers. What's more, images made from acoustical "scatterings" are suggestive of a massive fish aggregation. The 35-pound anglerfish shown here is one of the rare species hauled up from the deep during the project.

What did you expect? Would a colossal squid have anything but eyes big enough to generate a few over-the-top superlatives? Probably not - but still, when researchers thawed out this squid in New Zealand, the wow factor was undeniable. The creature's eye measured about 11 inches across; its lens was the size of an orange. Scientists suspect the big eye allows the huge squid to capture a lot of light in the dark depths in which it hunts. The squid weighed about 1,000 pounds when caught in the Antarctic's Ross Sea and measured 26 feet long. Scientists believe the species, which can descend to 6,500 feet, may grow as long as 46 feet.

Deep-sea corals record history

Rob Dunba
/
Stanford University

Some coral reefs are found thousands of feet below the ocean surface, where they have grown amid frigid waters for millennia. Like tree rings, they serve as a faithful archive of global environmental change, according to Robert Dunbar, a professor of geological and environmental sciences at Stanford University. His team travels the world to collect samples of these corals, such as this one from a colony near Easter Island. In 2007, the team published a 300-year archive of soil erosion in Kenya, as recorded by coral samples collected from the bottom of the Indian Ocean. They are now analyzing 4,000-year-old corals discovered off Hawaii to create an archive of climate change.

Trawling destruction visible from space

Sky Truth

Some scientists are working urgently to expose more secrets of the deep ocean before unexplored treasures are plundered. Their biggest concern is the fishing practice known as bottom trawling. This image shows the billowing plumes of sediment left in the wake of trawlers dragging giant nets across the ocean floor in the Gulf of Mexico. The practice has been shown to strip coral reefs bare and ravage underwater ecosystems such as seamounts, where thousands of species are known to gather. Though the practice is increasingly restricted, tens of thousands of trawlers continue to ply the deep oceans.